1. Field of the Invention
The present invention relates to a diffraction grating, and more particularly to a diffraction grating having a structure to control a sparkling phenomenon occurring in an image-reproducing apparatus due to a laser source.
2. Description of the Related Art
Generally, image-reproducing apparatuses such as projection televisions (TVs) and laser TVs, in order to produce various colors on a screen, use lasers capable of producing light beams of different wavelengths, with corresponding colors, such as red, green and blue. Color images are produced by combining the above-mentioned light beams of different wavelengths, and displaying them on a screen.
Laser beams produce light beams of different wavelengths and thus, different colors, which correspond to their respective wavelength. However, these light beams have a high coherency, so that an irregular intensity distribution is exhibited when the light beams reproduce an image on a display or screen. This irregular intensity distribution exhibited on the display or screen, due to the high coherency of the light beams, is called “sparkle noise.”
Such sparkle noise may be produced as a result of many factors, such as surface non-uniformity of the display or screen (on which an image is displayed by the light beams), and/or fine dust present in optical paths (along which the laser beams travel), and other factors.
Various means and methods have been proposed to attenuate or entirely abate this sparkle noise. For example, the use of ground glass plates has been proposed. In this case, the generation of sparkle noise on a display or screen is reduced by arranging the ground glass plates in the respective optical paths of different laser beams, and vibrating the ground glass plates. However, there is a problem in that the different light beams exhibit a loss of intensity after passing through the ground glass plates. Alternatively, as diffraction gratings are known to exhibit a high transmissivity with respect to the above-mentioned coherent light beams, as compared to ground glass plates, their use has also been proposed as a sparkle- noise-attenuating means. Diffraction gratings have an advantage in that they can reduce the intensity loss of the coherent light beams.
However, diffraction gratings for reducing or removing sparkle noise have the disadvantage of requiring a plurality of diffraction gratings, each having different grating periods corresponding to the respective wavelengths of the coherent light beams, which increases complexity and manufacturing costs and requires complex optical axis alignment due to use of a plurality of diffraction gratings.